This invention relates to the actuation of axisymmetric, variable area exhaust nozzles, and more particularly to improved synchronization of and fluid supply to flap mounted actuators.
Early jet engine exhaust nozzles were relatively short and required relatively low actuation forces. As nozzle designs improved, in order to achieve increased installed performance, the nozzles have generally increased in length which resulted in longer and heavier nozzle flaps which must be moved as the engine thrust and constants are changed during flight. It is not unusual for a force of 40,000 pounds to be required to move a set of nozzle flaps.
The high nozzle actuation forces required heavier actuation mechanisms and structures to transmit the increased forces, e.g., nozzle actuators, actuation rings, actuation mounting structures and force reacting structures. The heavier structures lead to inefficient aircraft design, since the weight of an engine exhaust nozzle is critical. This is particularly true in high performance aircraft in which the exhaust nozzles tend to be located at the rear of the aircraft rather than under the wings, so that the aircraft contours can be blended to exhaust nozzle contours resulting in a low drag, high performance installation. With the nozzles located at the rear of the aircraft, a relatively small weight change in the nozzle can result in a large effect in the aircraft weight distribution and balance. In some aircraft designs, it has been necessary to add weight in the nose of the aircraft to compensate for a tail heavy condition.
The heavier actuation mechanisms and force reacting structures can be eliminated by mounting the flap actuators directly on the flaps. The flap mounted actuators not only eliminate items such as actuation rings, cams and rollers, but reduce the force necessary to move the flaps. However, the actuation rings which are eliminated, also serve to synchronize the actuation of the flaps so as to retain the axisymmetric nozzle symmetry, i.e., essentially round.
There have been attempts to use flap mounted actuators such as the hydraulic actuation ring described in U.S. Pat. No. 4,181,260 assigned to the assignee of the present invention. The hydraulic actuation ring interconnects the nozzle flaps with an array of actuators. The motion of the actuators is synchronized by lubricated screws and gears, and unbalanced loading on the flaps is reacted by a system of guide rollers incorporated into the rigid actuator housing design. The hydraulic actuation ring requires extreme precision in manufacturing the segments of the array so that the actuators do not bind. The near perfect fit which is required also results in excessive manufacturing costs.
There have also been attempts to synchronize flap movement to maintain a nozzle in round when using apparently less rigid ring actuated flaps such as the flap synchronizing control described in U.S. Pat. No. 3,820,720. The synchronizing control consists of male and female members mounted on each flap so that male and female members on adjacent flaps engage. The synchronizing control tends to add rigidity to a flap array, but does not positively synchronize the movement of the flaps so that movement of any one flap is transmitted to all others.
The movement of the flap mounted actuators together with the flaps causes the fluid supply lines to the actuators to move and flex. While some minimal flexure of the supply lines can be tolerated, the elimination of supply line flexure, does away with the need for sturdier, heavier lines and a potential point of failure and maintenance.
While there have been improvements in exhaust nozzle design, still further improvements would be beneficial. These improvements would be particularly beneficial as they reduce the weight of the exhaust nozzle actuation mechanisms, improve manufacturing tolerances, improve reliability and reduce cost.